In fuel supply systems of internal combustion engines, the fuel is normally delivered with the aid of an electric fuel pump. The electric fuel pump is activated with the aid of the control unit of the internal combustion engine, respectively provided with voltage. During start-up of the internal combustion engine, the fuel pump runs as long as the control unit detects that the starting switch is actuated. If the internal combustion engine has been started, the pump remains switched on. If, on the other hand, the control unit detects that the internal combustion engine has not been set in operation or that an inadmissible operating state prevails, a safety switch is activated, which prevents fuel from being delivered when the ignition is switched on and the internal combustion engine is shutdown. In so doing, it is assured that the delivery of fuel is quickly stopped as, for example, would be the case after an accident.
Because it is required that an adequate fuel pressure is available immediately during start-up of the internal combustion engine, there are fuel supply systems, wherein a priming of the fuel pump occurs, the fuel pump already being supplied with voltage prior to the start-up of the internal combustion engine. Such a fuel supply system with a priming of the fuel pump is, for example, described in the publication EP 0 679 220 B1.
This known fuel supply system implements a priming of the fuel pump, whereat a determination is additionally made whether the expected start-up of the internal combustion engine deals with a regular start-up or a start-up after an initial filling of the fuel supply system, i.e. for example an initial start-up or a start-up after an extended shutdown of the internal combustion engine or after a repair is made to the fuel supply system. Provided that a replenishment of fuel to the fuel supply system has been detected, the duration of the priming of the fuel pump is lengthened with respect to a normal start-up.
By the use of such extended pump priming times, the fuel supply system is as a rule only partially evacuated of air; and as a result, an already existing air cushion in said fuel supply system is compressed. This is especially true for an initial filling of the fuel supply system with fuel. Moreover, the lower pressure as well as the high pressure system is not sufficiently filled with fuel, so that a plurality of injections is still required in order to purge the fuel supply system via the combustion chambers. This then leads to a relatively long start-up time of more than 25 s, especially for the so-called “original start-up” after the initial filling of the fuel supply system with fuel.